Ambient air is commonly used as a cooling medium in various types of heat exchanger applications ranging from the simple automotive radiator to large heat exchangers used in industrial processes. The operational capacity of such heat exchangers varies as a function of the temperature of the ambient air, and is therefor affected by seasonal or daily weather conditions.
At times, the ambient air temperature may rise too high for the heat exchanger to provide the required cooling capacity. In process applications, it may then become necessary to either temporarily suspend operation of the heat exchanger, or to utilize standby auxiliary cooling. However, auxiliary or mechanical cooling is expensive both in first cost and in operating cost. As an alternative, ambient air heat exchangers are sometimes provided with apparatus to spray water into their air passages to enhance their cooling capacity. The latent heat of vaporization required to evaporate the water droplets sprayed on the surfaces of the heat exchanger greatly increases the heat transferred from the other fluid flowing through the heat exchanger and provides the required cooling capacity when the ambient air temperature is too high.
Ambient air heat exchangers are also used with water spray apparatus on a continuous basis, where water is relatively abundant, to take advantage of the improvement in cooling capacity in those installations. For example, U.S. Pat. No. 2,485,849 discloses a heat exchanger or cooling tower provided with a plurality of liquid spray nozzles disposed above and adjacent to gas passages defined by undulating sheets. Gas flow across the undulating sheets through these passages is counter to the flow of liquid sprayed from the nozzles thereabove, and it is suggested that the turbulence introduced by the undulatins of these sheets facilitates greater contact between the liquid droplets in the spray, the liquid flowing down the sheets, and the gas moving upward through the passages. In the embodiment shown in the patent, water is used as the liquid, and air as the gas. Heat transfer occurs only between these two fluids, without provision for the cooling of a third fluid.
A problem noted in the above patent is the need to maximize contact between the liquid and gas moving through the common passages in order to obtain efficient heat transfer between the two. Similarly, when cooling a third fluid flowing through separate passages in a heat exchanger, it is especially important that the liquid, e.g., water, be distributed in a thin film over the outer surface of these separate passages and other adjacent surfaces within the heat exchanger, in order to maximize the heat transfer provided by evaporation of the liquid in the moving airstream. The spray nozzles or drip tube systems of the prior art do not provide adequate liquid distribution to achieve the desired uniform thin liquid film on these surfaces. Proper distribution of the liquid before it contacts the flowing gaseous fluid is the key to achieving a uniform liquid film and maximum heat transfer efficiency.
In consideration thereof, it is an object of this invention to provide a gas cooled heat exchanger wherein the evaporation of a liquid enhances the cooling of another fluid.
Another object of this invention is to provide means for uniformly distributing a thin film of liquid in the gaseous passages of the heat exchanger for effecting cooling of the other fluid by evaporation of the liquid film.
A further object of this invention is to provide means for maximizing the contact of the gaseous fluid with the liquid in the gaseous passages of the heat exchanger.
A still further object of this invention is to provide means for collecting any excess liquid which is not evaporated as it flows over the surfaces of the gaseous passages in the heat exchanger.
These and other objects of the present invention will be apparent from the description of the preferred embodiment and by reference to the attached drawings.